1. Field of the Invention
The present invention relates to a magneto-optical recording medium for recording data by heating with the use of a laser beam and reproducing it by means of the magneto-optical effect and a method of making the same.
2. Description of the Prior Art
A prior art magneto-optical recording medium is known having such a substantial arrangement as shown in FIG.7 or 8. In the arrangement, a magneto-optical recording layer 3 of a perpendicular magnetic anisotropy film, e.g. of amorphous rare-earth-transition-metal alloy film, which offers a relatively higher magneto-optical effect, is provided on a substrate 1 through a protective layer 2. The magneto-optical recording layer 3 is then covered with another protective layer 4 directly or through a reflective layer 5. In operation, the recording and erasing procedures are carried out, in a thermomagnetic manner, by locally heating the magneto-optical recording layer 3 to over a compensation temperature or about a curie temperature with the irradiation of a laser beam 6 onto the magneto-optical recording medium and simultaneously, applying an external magnetic field 7 in a direction at right angle to the layer 3. Also, the reproduction is made by irradiating linearly polarized weak power laser beam 6 onto the magneto-optical recording layer 3 carrying recorded data and detecting the direction of magnetization in the incident area by means of the Kerr magneto-optical effect or the Faraday (magneto-optical) effect.
Specifically, there are two methods for magneto-optical recording-an optical modulation recording method for recording by modulating the irradiating laser beam power according to a signal to be recorded under a specific recording magnetic field strength, and a magnetic-field modulation recording method for recording by modulating the direction of the recording magnetic field according to a signal to be recorded under a specific constant laser power irradiation.
The disadvantages of the foregoing prior art magneto-optical recording medium are that, particularly in recording and erasing as follows:
1) A relatively greater rate of the external magnetic field intensity (e.g. about 300 Oe for the magneto-optical recording layer of TbFeCo) is needed for satisfactory saturation of the S/N (signal-to-noise) ratio of a reproduced signal, thus causing the magnetic field supplying device of a recording apparatus to be bulky in size or making it difficult to use a magnetic-field modulation recording method which requires a frequency range of some megahertz in the magnetic field. PA1 2) The required intensity of the external magnetic field varies depending on the area of the magneto-optical recording layer.